1. Field of the Invention
Embodiments of the present invention relate generally to treatment of valvular regurgitation, such as, for example, involving the use of a transvalvular band to treat aortic regurgitation.
2. Description of the Related Art
The heart is a double (left and right side), self-adjusting muscular pump, the parts of which work in unison to propel blood to all parts of the body. The right side of the heart receives poorly oxygenated (“venous”) blood from the body from the superior vena cava and inferior vena cava and pumps it through the pulmonary artery to the lungs for oxygenation. The left side receives well-oxygenated (“arterial”) blood from the lungs through the pulmonary veins and pumps it into the aorta for distribution to the body.
The heart has four chambers, two on each side—the right and left atria, and the right and left ventricles. The atria are the blood-receiving chambers, which pump blood into the ventricles. A wall composed of membranous and muscular parts, called the interatrial septum, separates the right and left atria. The ventricles are the blood-discharging chambers. A wall composed of membranous and muscular parts, called the interventricular septum, separates the right and left ventricles.
The synchronous pumping actions of the left and right sides of the heart constitute the cardiac cycle. The cycle begins with a period of ventricular relaxation, called ventricular diastole. The cycle ends with a period of ventricular contraction, called ventricular systole.
The heart has four valves that ensure that blood does not flow in the wrong direction during the cardiac cycle; that is, to ensure that the blood does not back flow from the ventricles into the corresponding atria, or back flow from the arteries into the corresponding ventricles. The valve between the left atrium and the left ventricle is the mitral valve. The valve between the right atrium and the right ventricle is the tricuspid valve. The pulmonary valve is at the opening of the pulmonary artery. The aortic valve is at the opening of the aorta.
Various disease processes can impair the proper functioning of one or more of these valves. These include degenerative processes (e.g., Barlow's Disease, fibroelastic deficiency), inflammatory processes (e.g., Rheumatic Heart Disease) and infectious processes (e.g., endocarditis). In addition, damage to the ventricle from prior heart attacks (i.e., myocardial infarction secondary to coronary artery disease) or other heart diseases (e.g., cardiomyopathy) can distort the valve's geometry causing it to dysfunction.
The mitral valve is comprised of an anterior leaflet and a posterior leaflet. The bases of the leaflets are fixed to a circumferential partly fibrous structure, the annulus, preventing dehiscence of the valve. A subvalvular apparatus of chordae and papillary muscles prevents the valve from prolapsing into the left atrium. Mitral valve disease can be expressed as a complex variety of pathological lesions of either valve or subvalvular structures, but can also be related to the functional status of the valve. Functionally the mitral valve disease can be categorized into two anomalies, increased leaflet motion i.e. leaflet prolapse leading to regurgitation, or diminished leaflet motion i.e. restricted leaflet motion leading to obstruction and/or regurgitation of blood flow.
Leaflet prolapse is defined as when a portion of the leaflet overrides the plane of the orifice during ventricular contraction. The mitral regurgitation can also develop secondary to alteration in the annular ventricular apparatus and altered ventricular geometry, followed by incomplete leaflet coaptation. In ischemic heart failure this can be attributed to papillary or lateral wall muscle dysfunction, and in non-ischemic heart failure it can be ascribed to annular dilation and chordal tethering, all as a result of dysfunctional remodeling.
The predominant cause of dysfunction of the mitral valve is regurgitation which produces an ineffective cardiac pump function resulting in several deleterious conditions such as ventricular and atrial enlargement, pulmonary hypertension and heart-failure and ultimately death.
The main objective for the surgical correction is to restore normal function and not necessarily anatomical correction. This is accomplished by replacing the valve or by reconstructing the valve. Both of the procedures require the use of cardiopulmonary bypass and is a major surgical operation carrying a non-negligible early morbidity and mortality risk, and a postoperative rehabilitation for months with substantial postoperative pain. Historically, the surgical approach to patients with functional mitral regurgitation was mitral valve replacement, however with certain adverse consequences such as thromboembolic complications, the need for anticoagulation, insufficient durability of the valve, loss of ventricular function and geometry.
Reconstruction of the mitral valve is therefore the preferred treatment for the correction of mitral valve regurgitation and typically consists of a quadrangular resection of the posterior valve (valvuloplasty) in combination with a reduction of the mitral valve annulus (annuloplasty) by the means of suturing a ring onto the annulus. These procedures are surgically demanding and require a bloodless and well-exposed operating field for an optimal surgical result. The technique has virtually not been changed for more than three decades.
More recently, prolapse of the valve has been repaired by anchoring the free edge of the prolapsing leaflet to the corresponding free edge of the opposing leaflet and thereby restoring apposition but not necessarily coaptation. In this procedure a ring annuloplasty is also required to attain complete coaptation.
This method commonly referred to as an edge-to-edge or “Alfieri” repair also has certain drawbacks such as the creation of a double orifice valve and thereby reducing the effective orifice area. Several less invasive approaches related to the edge-to-edge technique has been suggested, for repairing mitral valve regurgitation by placing a clip through a catheter to suture the valve edges. However, it still remains to conduct an annuloplasty procedure, which has not yet been resolved by a catheter technique and therefore is to be performed by conventional surgery, which makes the method impractical.
Notwithstanding the presence of a variety of presently available surgical techniques and promising catheter based procedures for the future, there remains a need for a simple but effective device and corresponding surgical, minimally invasive or transvascular procedure to reduce mitral valve regurgitation.